Modern concepts in industrial automation engineering, that is to say in the control and monitoring of technical processes using software, are based on the idea of a central control with a distributed sensor/actuator level. In this case, the subscribers communicate with one another and with superordinate systems via industrial data networks, subsequently also referred to as automation networks.
The Ethernet is the most widely used communication standard in local area networks (LANs) and is stipulated primarily by IEEE standard 802.3. The Ethernet is based on a LAN design, in which a plurality of control nodes, for example computers or machines, are connected to one another by cable, with the Ethernet protocol performing the encapsulation of the data to be transmitted in data packets, subsequently also referred to as a message, having a predetermined format. Different Ethernet variants can be used in this case that differ in terms of the transmission rate, the cable types used and the line encoding.
In the case of Ethernet networks used in industry, the communication between the subscribers normally travels via a data line having four wires, the four wires often being embodied as two twisted wire pairs. The twisting of the wire pairs reduces crosstalk. The two wires of a wire pair are always used together, with a differential data signal being transmitted via a respective wire pair. Sometimes, all four wires are also twisted together, which admittedly results in disadvantages for electromagnetic compatibility, but has the advantage of greater flexibility for the line.
A frequently imperative demand on automation networks is that the outputs of a machine, the actuators, can be put into a safe state at any time without losing the capability of monitoring the machine in the process. The sensors and the control in the automation network therefore need to be able to be operated independently of the actuators. For this reason, a power supply for the actuators is normally embodied separately from the power supply for the sensors or the control in order to perform a shutdown of the actuator supply independently of the sensor or control supply.
The power supply lines needed in the automation network are normally laid independently of the data line, this necessitating at least two dedicated wirings using the appropriate contact technology. In industrial automation, however, it is desirable to always achieve the most inexpensive and simple wiring possible in the automation network. This is important particularly when environmental needs mean that good shielding, a high protection class or high heat resistance is required for the wiring. The wiring is therefore often responsible for a relevant high proportion of the system costs.
One approach to save costs for the wiring involves combining the power supply and the data transmission in one wiring. It is thus possible to use the “Power over Ethernet” (PoE) standard to transmit a single voltage via a four-wire standard Ethernet data line in addition to the two differential data signals on the two twisted wire pairs as well. In the case of the PoE standard, this is accomplished by using a specially adapted Ethernet transformer that applies the two potentials required for the voltage to one wire pair each via a central tap. Since two separate power supplies are frequently required in industrial automation, however, one for the actuators and the other for the sensors or the control, even a PoE system with a four-wire data line requires additional wiring for a second power supply.
The concept of the PoE system can be transferred to automation engineering, so that a user can be provided with the capability of connecting automation engineering devices (for example input/output modules) to just one instead of the otherwise usual two lines (communication and power supply). To this end, the supply voltage and the data signal are transmitted on the same line and separated from one another by means of an electronic circuit.
Devices that have this technology cannot thus readily be connected to devices that do not have this technology, since the devices that do not have this technology would otherwise have a supply voltage applied to the communication components, which can lead to (irreparable) damage in the device.
The laid-open specification US 2013/0093444 A1 and the patent specification U.S. Pat. No. 6,218,930 B1 each show a way of detecting capabilities of remote devices.